RFR(XXS) 8201321: NMT: Unnecessary re-recording thread stack and size when attaching listener to JavaThread

[Zhengyu Gu]

Hi,

Please review this trivial change, that removed unnecessary call to 
record Java thread, which should already be done. Also, added assertion 
to ensure it is the case.

This line was added during early NMT work, and it is redundant.

Bug:  https://bugs.openjdk.java.net/browse/JDK-8201321
Webrev: http://cr.openjdk.java.net/~zgu/8201321/webrev.00/

Test:

  hotspot_runtime on Linux x64 (release and fastdebug)
                     Windows x64 fastdebug

  Submit-hs tests.

Thanks,

-Zhengyu